1. Field of the Invention
The present invention relates to a device for measuring a fill level of a liquid in a container, more specifically in a fuel tank of a motor vehicle. The device comprises a measuring tube with compensating openings and an ultrasonic sensor arranged proximate an end of the measuring tube for generating ultrasonic waves in the measuring tube and for receiving reflections of the ultrasonic waves reflected in the region of the liquid level in the container.
2. Description of the Related Art
Devices for measuring the fill level of fuel in a fuel tank using ultrasonic sensors are known in which an ultrasonic sensor has an outside diameter corresponding to the inside diameter of a measuring tube arranged in the fuel tank. The ultrasonic sensor is plugged into an end of the measuring tube. The measuring tube penetrates the bottom of the container and is filled with the liquid present in the fuel tank via compensating bores. To amplify the ultrasonic waves reflected by the liquid level, a float for reflecting the ultrasonic waves is arranged in the measuring tube. The sides of the measuring tube shield the ultrasonic sensor from lateral reflections which could degrade the measurement results.
A disadvantage of the known device that the ultrasonic sensor contacts the liquid in the container and the container must be sealed in a complicated fashion. Accordingly, the ultrasonic sensor for measuring a fill level in a fuel tank requires a very complicated and expensive encapsulation.
One solution to avoid sealing the bottom of the container in the area of the sensor includes a device in which the measuring tube with the ultrasonic sensor is arranged on a cover lid of the container and dips into the liquid. However, containers such as fuel tanks produced from plastic for motor vehicles, in particular, can swell and become deformed as a function of the fill level of the fuel. The deformation may raise or lower the bottom of the container and produce erroneous measurements of the fill level.
An object of the present invention is to provide a device for measuring the fill level of a container via reflections of an ultrasonic wave detected by a sensor such that it detects the fill level with particular reliability and requires no complicated sealing of the ultrasonic sensor or of the container.
The object of the present invention is met by a container having a measuring tube arranged therein such that a subregion of a container wall of the container is arranged between the measuring tube and an ultrasonic sensor.
This configuration reliably protects the ultrasonic sensor against contact with the liquid located in the container. Accordingly, the ultrasonic sensor cannot be attacked by the liquid located in the container. Furthermore, sealing in the wall of the container is not required because the wall of the container is not penetrated by the measuring tube. The device according to the present invention allows a particularly reliable measurement of the filling level in the container. Furthermore, the device according to the present invention comprises a simple design that can be produced very cost-effectively. Of course, a float may optionally be arranged in the measuring tube as is known.
The design of the device according to the present invention may be simplified by assembling the ultrasonic sensor and an evaluation unit for the signals of the ultrasonic sensor as one structural unit. In addition, the configuration as one structural unit simplifies mounting of the device on the container.
The measuring tube is preferably arranged vertically in the container. However, the measuring tube may alternatively be arranged at a slant in the container. In addition, the ultrasonic sensor could optionally be arranged on the top side of the container for determining the fill level of the liquid in the container by comparison of the ultrasonic waves reflected by the bottom and the ultrasonic waves reflected by the liquid level. However, the device according to the present invention requires only a particularly cost-effective and simply designed evaluation unit when the ultrasonic sensor bears directly against the subregion of the wall of the container constructed as a bottom of the wall of the container.
In accordance with another advantageous embodiment of the present invention, the ultrasonic sensor is securely fastened on the container and exhibits reliable transmission of sound onto the wall of the container when the ultrasonic sensor is permanently bonded to the wall of the container.
In accordance with another advantageous embodiment of the present invention, the ultrasonic sensor and the evaluation unit are protected against soiling and damage by a housing for holding the ultrasonic sensor and/or the evaluation unit of the ultrasonic sensor. This configuration extends the life of the ultrasonic sensor and of the evaluation unit when they are provided for a fuel tank mounted under a motor vehicle body.
In accordance with another advantageous embodiment of the present invention, the housing of the ultrasonic sensor is filled with a contact means which is a good conductor of ultrasonic waves for further improving the introduction of the sound into the wall of the container.
The measuring tube may, for example, be produced from metal. However, in accordance with another advantageous embodiment of the invention the measuring tube may be produced from plastic via injection molding with virtually any desired cross section. Accordingly, the shape of the measuring tube may, for example, be round, oval, or polygonal in accordance with the dimensions of an ultrasonic sensor and of an ultrasonic receiver of the ultrasonic sensor. The device according to the present invention may thereby be produced in a particularly cost-effective way.
A further reduction in the production costs of the device according to the present invention may be effected by producing the measuring tube as one piece with the container. If the container is produced from plastic via injection molding, the production of the measuring tube as one piece with the contianer requires no additional production steps.
In accordance with another advantageous embodiment of the present invention, support elements are arranged in the container for laterally supporting the measuring tube so that the measuring tube may be arranged easily in containers of virtually any desired shape.
One end of the measuring tube may be connected permanently to the container. However, the second end of the measuring tube may vibrate freely which produces a foaming in the region of the fill level of the liquid. This foaming produces inaccuracies in the measurement of the fill level. In accordance with another advantageous embodiment of the present invention, the measuring tube is reliably protected against vibrations when the measuring tube is held by two mutually opposite walls of the container.
In accordance with another advantageous embodiment of the present invention, the measuring tube forms a structural unit with a component that is to be arranged in the container so that the measuring tube may be mounted with particular ease.
When the container comprises a fuel tank for a motor vehicle, the lower end of the measuring tube is located end near the deepest point when the measuring tube is arranged on a splash pot or a suction jet pump of the fuel tank. The splash pot may be prestressed against the bottom of the fuel tank or may be produced in one piece with the tank so that the filling level in the fuel tank may be detected particularly reliably.
The production costs may be minimized and the mounting of the device simplified when the measuring tube is produced in one piece with the splash pot or a holder for the splash pot.
Fuel tanks of present-day motor vehicles are frequently constructed as saddle tanks or other types of multichamber tanks. In these configurations, the reliable determination of the fill level of the liquid is particularly easily obtained when the container has a plurality of ultrasonic sensors bearing against the outside of the container such that one ultrasonic sensor is associated with each of the chambers of the tank.
When the container is virtually full, a float facilitates operation by amplifying the ultrasonic signals reflected by the liquid level. However, when the container is near empty, the float falsifies the fill level determined. Therefore, a further embodiment of the present invention comprises a stop arranged in the measuring tube for bounding the float below a range of movement so that the fill level may be determined equally reliably when the container is fill and when the container is empty. Furthermore, a reserve fill level may be fixed very easily by the height of the stop. If the fill level in the container is below the stop for the float, the ultrasonic sensor receives two reflections irrespective of the type and temperature of the fuel. The fill level of the virtually empty fuel tank can be determined particularly accurately by comparing the two reflections.
In accordance with another embodiment of the present invention, compensating openings having a damping element for damping the pressure compensation are arranged at at least one end of the tube for preventing foaming in the measuring tube. Furthermore, fluctuations in the liquid column in the measuring tube are reliably damped thereby.